1. Field of the Invention
The present invention relates generally to elevating work platforms and, more particularly, to safety devices for detecting translation of the elevated platform in scissor lift apparatus and for maintaining the apparatus within balance.
2. Description of the Prior Art
Prior devices for maintaining the balance of elevating work platforms have been known in the art dealing with articulated booms. An example of such prior device is shown in U.S. Pat. No. 4,081,055. This device senses the vertical position of the boom in reference to the horizon. In response to an out-of-balance condition it disables the hydraulic system to prevent further movement of the boom. This is accomplished by providing the boom with a chain and sprocket mechanism whereby the position of the chain indicates the position of the articulated boom. Further, there is provided a position-indicating marker on the chain and a corresponding sensing plunger whereby predetermined movement of the chain actuates the plunger to signify out-of-limit travel.
Heretofore, no such device has been proposed for an elevating platform raised by a scissors mechanism. In such a system the out-of-balance condition of the platform depends upon the relative position of both scissors members. Accordingly, there is generally provided in the present invention mechanical means for sensing the relative position of the extending scissors members and for mechanically determining the relative horizontal shift of the platform. On sensing this shift appropriate automatic adjustments are made to the hydraulic lift system to return the platform to a balanced position.